Cancer is one of the most challenging disorders to treat in modern medicine for several reasons. Since cancer arises from the abnormal behavior of one's own cells, distinguishing cancer cells from normal cells within a patient is a difficult problem. Often the body's own immune system has difficulty identifying and eliminating cancerous cells. In addition, “cancer” refers to a constellation of individual disorders, i.e., types and subtypes of cancer. Many different cell types can become cancerous through many different mechanisms, resulting in a tremendous phenotypic variety in the types of cancer cells that may arise. This diversity is highly problematic for cancer treatment because different types of cancer cells may have different identifying properties for diagnosis, or they may possess different therapeutic weaknesses or resistant properties. This problem makes it difficult to come up with ways to diagnose, treat, and/or prevent multiple types of cancer through a single therapeutic strategy or agent. Even though oncology has advanced tremendously in the last decade, there is still a need to identify new biomarkers specific to cancer cells, particularly biomarkers that characterize multiple types of cancer but not normal tissues.
Cell surface molecules are highly important for cancer cells. These molecules are critically involved in cell-cell interactions, which are important for many cancer cell behaviors, including cell invasion, metastasis, evasion of the immune system, and responses to therapeutic agents. Cancer cells are known to express many cell surface proteins differently from normal cells. However, many cell surface proteins are modified by the addition of saccharides (e.g., N-acetylglucosamine or N-acetyl-galactosamine), a process termed protein glycosylation. How specific cell surface proteins are modified by the addition of saccharides, which saccharides may be found on which cell surface proteins, and how patterns of glycosylation change during different types or phases of carcinogenesis are all problems that are just beginning to be explored (for a review, see Moremen, K. W., et al. (2012) Nat. Rev. Mol. Cell Biol. 13(7):448-62). This diversity in glycosylation increases the complexity of cancer cell recognition by surface biomarkers. Therefore, there remains a need for new biomarkers and therapeutic agents useful in the diagnosis, treatment, and prevention of cancer, particularly for biomarkers and agents that target cancer-specific patterns of glycosylation.
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